I. Field of the Invention
The present invention relates to data communication. More particularly, the present invention relates to a novel and improved pilot reference transmission scheme for use in a wireless communication system.
II. Description of the Related Art
In a wireless communication system, a pilot reference is often transmitted from a transmission source to a receiving device to assist the receiving device performs a number of functions. The pilot reference is typically a predetermined data pattern processed (e.g., covered and spread) in a known manner. The pilot reference can be used at the receiving device to estimate the quality of the transmission link, coherently demodulate the received transmissions, and perform other functions.
A wireless communication system such as a code division multiple access (CDMA) system or a time division multiple access (TDMA) system (e.g., a Global System for Mobile Communications (GSM) system) typically includes a number of base stations that transmit to a number of remote terminals. Each base station is designed to cover a particular coverage area and transmits to the remote terminals within its coverage area. For systems in which neighboring base stations transmit on the same frequency band to improve spectral efficiency, such as many CDMA-based systems, the transmissions from each base station act as interference to those of neighboring base stations, and possibly to its own transmissions due to multipath. This interference degrades the quality of the transmissions received at a remote terminal, including the pilot transmission.
For the conventional IS-95 CDMA system, a pilot reference is continuously transmitted on a dedicated pilot channel at a particular (relatively low) transmit power level. The remote terminal receives and processes the forward link signal to isolate the pilot channel, and further processes the pilot channel to recover the pilot reference. The interference from these other transmissions can affect the quality of the received pilot reference. This interference is worse when the orthogonality between the pilot channel and the traffic channels used for the data transmissions is lost due to, for example, multipath.
The pilot reference transmission scheme used for the IS-95 CDMA system is adequate for voice communication since the data rate is low, which allows the remote terminal more time to process the pilot reference. However, for a high-speed data transmission system in which the link condition is required to be accurately estimated within a short period of time, this continuous low-level pilot reference is not adequate.
As can be seen, a pilot reference transmission scheme that can provide a high quality pilot reference to the remote terminals and allow a remote terminal to quickly and accurately estimate the link condition is highly desirable.